This thesis investigates the ways in which hereditary degeneration was discussed by Scottish psychiatrists in the late nineteenth and early twentieth centuries with particular reference to the anti-alcohol debate. I examine the theoretical writings of both clinical and forensic psychiatry to show how the theory of degeneration functioned as part of a new understanding of legal medicine and that psychiatric knowledge was always implicitly related to a broader conception of criminal capacity and the role of the modern state. While the argument is situated in the wider literature covering psychiatry and degeneration in Europe and America during the late nineteenth and early twentieth centuries, I trace a rather singular story rooted in the institutional peculiarities of Scotland, showing how psychiatrists attempted to use the problem of alcoholic degeneration to mould their science into a branch of public health, propelling them into their preferred role as guardians of the race. This public health campaign facilitated the creation of new categories of psychiatric knowledge consisting of mental abnormalities that did not amount to absolute insanity, but that none the less had a bearing on how people thought about the mind, conduct, and criminal capacity. All the leading figures of Scottish psychiatry had a significant interest in alcohol as a cause of degeneration, and in their descriptions of the condition, the legal applications of the doctrine were never from view. One reason for this was undoubtedly the autonomous nature of the Scottish legal system which, when combined with the relatively small professional population of Scotland, greatly increased the rate of intellectual exchange between psychiatrists and lawyers while intensifying the political implications of associating with certain doctrines. Thus, a large part of my thesis will also be devoted to the legal interpretation of psychiatric claims, and in later part of the thesis I examine in depth the extent to which psychiatric knowledge claims were able to modify the laws of Scotland. Three substantive themes protrude from the documents consulted: Heredity, degeneration and alcohol, and medico-legal interaction. In analysing these themes, I engage with specific aspects of the social and institutional life of Scottish psychiatrists in the late-nineteenth and early-twentieth centuries.